Consistency measuring apparatus is well known in the paper processing industry, the apparatus being designed to detect the consistency of the pulp flowing through a pipe, and to provide some indication of that consistency. Such consistency measuring apparatus generally includes a sensor blade disposed in the pipe so the blade is subjected to the pulp as the pulp flows through the pipe. The sensor blade is carried by an arm, the arm being pivotally mounted with respect to the pipe, so motion of the arm can be detected to give an indication of the consistency. Since the arm is pivotal with respect to the pipe, it will be understood that flexible sealing means is used to allow the motion while retaining the liquid within the pipe.
The sealing means in the prior art apparatus is a source of some problems. It will be understood that small rocks or other hard substances are sometimes in the pipe line, and these hard substances can hit the flexible seal and damage the seal. Also, heat and time will eventually cause damage to the seal so the seal will leak. The electronic measuring apparatus is normally in a single housing with the end of the arm of the sensor plate. so leakage may destroy all the electronic measuring apparatus.
The conventional technique for detecting motion of the arm comprises a variable capacitor. One group of plates is fixed with respect to the pipe, and the other group of plates is movable by the arm carrying the sensor plate. As a result, when the sensor arm moves, the group of capacitor plates moves, changing the capacitance of the variable capacitor. Well known electronic circuitry can then be used to detect the change in capacitance, and to calibrate the change in terms of consistency. Because of this technique, it will be understood that the electronics must be mounted at the consistency measuring device, and cannot be removed to a more distant, safe, location. Also, the device must always be returned to "zero" before making subsequent measurements.